Re: 2.5.20 RAID5 compile error

[Horst von Brand]

Martin Dalecki <[e-mail]> said:
> Well it's kind like the answer to the question: why don't do it all in hand
> optimized assembler? Or in other words - let's give the GCC guys good
> reasons for more hard work. But more seriously:
> 
> Things like unlikely() tricks and other friends seldomly really
> pay off if applied randomly. But they can:
> 
> 1. Have quite contrary effects to what one would expect due to
> the fact that one is targetting a single instruction set but in
> reality multiple very different CPU archs or even multiple archs.
> 
> 2. Changes/improvements to the compiler.
> 
> My personal rule of thumb is - don't do something like the
> above unless you did:
> 
> 1. Some real global profiling.
> 2. Some real CPU cycle counting on the micro level.
> 3. You really have too. (This should be number 1!)

Anybody trying to tune code should read (and learn by heart):

@Book{bentley82:_writing_eff_progr,
  author =	 {Jon Louis Bentley},
  title = 	 {Writing Efficient Programs},
  publisher = 	 {Prentice Hall},
  year = 	 1982
}

(sadly out of print AFAIK)
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
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